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| author | Andy Lutomirski <luto@kernel.org> | 2017-02-20 19:56:14 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-02-21 14:45:08 +0300 |
| commit | b7ffc44d5b2ea163899d09289ca7743d5c32e926 (patch) | |
| tree | c41439937c5810b701a895d1f9e060b57573d540 /arch/x86/kvm/vmx.c | |
| parent | d3273deac9c0cdae32eb46f928487433eaa37f87 (diff) | |
| download | linux-b7ffc44d5b2ea163899d09289ca7743d5c32e926.tar.xz | |
x86/kvm/vmx: Defer TR reload after VM exit
Intel's VMX is daft and resets the hidden TSS limit register to 0x67
on VMX reload, and the 0x67 is not configurable. KVM currently
reloads TR using the LTR instruction on every exit, but this is quite
slow because LTR is serializing.
The 0x67 limit is entirely harmless unless ioperm() is in use, so
defer the reload until a task using ioperm() is actually running.
Here's some poorly done benchmarking using kvm-unit-tests:
Before:
cpuid 1313
vmcall 1195
mov_from_cr8 11
mov_to_cr8 17
inl_from_pmtimer 6770
inl_from_qemu 6856
inl_from_kernel 2435
outl_to_kernel 1402
After:
cpuid 1291
vmcall 1181
mov_from_cr8 11
mov_to_cr8 16
inl_from_pmtimer 6457
inl_from_qemu 6209
inl_from_kernel 2339
outl_to_kernel 1391
Signed-off-by: Andy Lutomirski <luto@kernel.org>
[Force-reload TR in invalidate_tss_limit. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx.c')
| -rw-r--r-- | arch/x86/kvm/vmx.c | 23 |
1 files changed, 9 insertions, 14 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 2dd94cf597cc..acf6013a0caf 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -1990,19 +1990,6 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr, m->host[i].value = host_val; } -static void reload_tss(void) -{ - /* - * VT restores TR but not its size. Useless. - */ - struct desc_ptr *gdt = this_cpu_ptr(&host_gdt); - struct desc_struct *descs; - - descs = (void *)gdt->address; - descs[GDT_ENTRY_TSS].type = 9; /* available TSS */ - load_TR_desc(); -} - static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset) { u64 guest_efer = vmx->vcpu.arch.efer; @@ -2172,7 +2159,7 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx) loadsegment(es, vmx->host_state.es_sel); } #endif - reload_tss(); + invalidate_tss_limit(); #ifdef CONFIG_X86_64 wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base); #endif @@ -2293,6 +2280,14 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) (unsigned long)this_cpu_ptr(&cpu_tss)); vmcs_writel(HOST_GDTR_BASE, gdt->address); + /* + * VM exits change the host TR limit to 0x67 after a VM + * exit. This is okay, since 0x67 covers everything except + * the IO bitmap and have have code to handle the IO bitmap + * being lost after a VM exit. + */ + BUILD_BUG_ON(IO_BITMAP_OFFSET - 1 != 0x67); + rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp); vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */ |